NEUTRINO AND GEN IV REACTOR SYSTEMS · 2020. 11. 24. · Reactor Neutrino Experiment, for which he shared the 2016 Breakthrough Prize for Fundamental Physics for his contributions

NEUTRINO AND GEN IV REACTOR SYSTEMS

Prof. Jonathan LinkVirginia Tech, USA19 November 2020

Meet the PresenterProf. Jonathan Link received his Ph.D. in particle physics from the University of California Davis in 2001 and was a postdoctoral fellow at Columbia University before joining the Department of Physics at Virginia Tech as a faculty member in 2006. He also has an appointment of affiliated faculty in Virginia Tech’s Nuclear Engineering Program.Prof. Link has been part of several experimental collaborations, including the Daya Bay Reactor Neutrino Experiment, for which he shared the 2016 Breakthrough Prize for Fundamental Physics for his contributions to their discovery of the final neutrino mixing angle. Currently, Prof. Link is leading an effort to develop a new reactor neutrino detector technology known as CHANDLER, which recently published their first observation of reactor neutrino. The prototype detector used in this study was one of the world’s smallest neutrino detectors, and the first mobile reactor neutrino detector. Prof. Link is a member of the executive group for the NNSA-funded NuTools study, which seeks to examine the potential for applications of neutrino detection to nuclear non-proliferation and the nuclear industry.

Email: [email protected]

What This Talk Will Cover

The History of Neutrinos and Reactors

Possible Applications of Neutrino Detection

Recent Advances in Neutrino Detector Technology

But first, a disclaimer…

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DisclaimerI am a particle physicist, not a nuclear engineer.

We physicist imagine ourselves to be quite clever, but we can be surprisingly naive about the real world.

We hope that our technology can help to bring about a low-carbon future, by enhancing the safety, security, and/or efficiency of nuclear power, but none of us really knows how neutrinos could best be used in the nuclear industry.

The point of this talk is to raise awareness within the GEN IV community about the information available through reactor neutrino detection, and the relative easy or difficulty of extracting that information.

My hope is that this community can help to identify appropriate problems where neutrino detectors may be a constructive part of the solution.

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The Invention of Neutrinos Neutrinos were first proposed by Wolfgang Pauli in 1930 in an attempt to save energy conservation in beta decay.

83210Bi → 84210Po + 𝑒𝑒−

Wolfgang Pauli

Eβ

Even

ts

+ ν

Adding a third particle in the final state makes it possible for the beta to have any energy less than the maximum.

In order for this particle to go unseen, it had to have no charge, no mass, and a very weak interaction strength: a completely new and unknown type of particle…

And it would be nearly impossible to detect.

Q

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Discovery of the NeutrinoReines and Cowan monitoring their neutrino

discovery experiment in 1956.

Neutrinos were not discovered until 26 years later.

Fred Reines and Clyde Cowan lead the discovery experiment at Savannah River’s P Reactor.

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Reactors as a Neutrino Source

U23592Typical Fission

eνBa14056 ++ β

eνLa14057 ++ β

eνCe140

58 ++ β

eνSr194

38 ++ β

eνY194

39 ++ β

eνZr9440 ++ β

n

n

n

Cs14055Rb9437

7

Nuclear reactors are an intense source of electron antineutrinos (�ν𝑒𝑒). They come from the beta decay of the neutron-rich fission fragments.

A 3 GW thermal reactor produces 6×1020 �ν𝑒𝑒 per second.

Reactors as a Neutrino SourceThe neutrinos are emitted isotopically, so their intensity falls off as ⁄1 𝑟𝑟2.

They are so weakly interacting that they are unaffected by shielding.

They carry information about the fission in the core, like the reactor power, the spatial distribution of fission, and the mix of fissile elements present.

With enough detector mass you could track burn-up from outside the secondary containment, or even outside the security perimeter.

This tracking requires no input from the operators, and has no impact on reactor operations.

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Reactor Neutrino DetectionElectron antineutrinos can be detected through a process known as inverse beta decay:

𝑝𝑝 + �ν𝑒𝑒 → 𝑛𝑛 + 𝑒𝑒+

Organic scintillators are typically used as the detection medium, because they contain lots of free protons, in the from of hydrogen nuclei.

Inverse beta decay results in a delayed coincidence signature.

The positron is detected promptly, while the neutron thermalize before it is captured, resulting in a delayed signal.

In an undoped scintillator the neutron will capture on hydrogen, but often the scintillator is doped with things like gadolinium or lithium-6 to enhance capture.

(with a 1.8 MeV Threshold)

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Reactor Neutrino BackgroundsThe weak signal from neutrino interactions can easily be overwhelmed by cosmic-rays and conventional radiation.

The delayed coincidence eliminates the vast majority of background.

The remaining backgrounds are things like random coincidences and cosmic-ray fast neutrons.

A fast neutron hits a proton in the scintillator causing a recoil that mimics the positron in an inverse beta decay.

The coincidence is completed when the neutron thermalizes and is captured in the detector.

The Daya Bay Reactor Neutrino Experiment

To control backgrounds, neutrino detectors are often located deep underground and surrounded by layers of low activity shielding materials.

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Reactor Neutrino Backgrounds

Random coincident events have no structure in the time separation between the prompt and delayed signals,

But correlated events, including fast neutrons and inverse beta decay, have an exponentially decaying neutron capture time.

As a result, fast neutrons are the more serious background concern.

Random Coincident Events

Correlated Events

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Discovery of the NeutrinoReines and Cowan used a layered detector to pick out the specific signatures of the positron and neutron from inverse beta decay.

Reines and Cowan’s Savannah River Detector

By tagging the positron annihilation gammas, they filtered out fast neutrons.

12 meters underground

11 meters from the reactor

Used cadmium for neutron capture

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Neutrino Physics at ReactorsSince the original discovery experiment, there have been dozens of distinct reactor neutrino experiments.

Among other things, they have • Studied different types of neutrino interactions, • Searched for the neutrino magnetic moment, and • Searched for and studied neutrino oscillations.

Neutrino oscillations are the most important discovery in particle physics in the last 40 years, and this is where reactor neutrinos have made their greatest contribution to science.

Before discussing this, we’ll need a quick introduction to particle physics…

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Particle PhysicsParticle physics is the study of fundamental particle and forces.

There are four fundamental forces:

1. Gravity

2. Electromagnetism

3. The Strong Nuclear Force

4. The Weak Nuclear Force

Neutrino interactions are weak because they only feel the Weak Nuclear Force (and perhaps gravity, but that’s not relevant at the scale of particle physics).

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Neutrinos and Particle Physics

The spin ½ particles include 6 quarks and 6 leptons.

These come in three generations which get progressively heavier, but otherwise have the same properties.

The spin 1 gauge bosons which mediate the forces.

The Higgs boson is responsible for giving the other particles mass.

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Neutrinos and Particle PhysicsAn

timat

ter

Every particle has an antimatter counterpart.

We denote antimatter with a bar.

Antimatter particles have the opposite sign charge relative to their matter counterpart.

The neutral bosons are their own antimatter.

But there are both neutrinos and antineutrinos.

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Neutrinos and Particle Physics

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Neutrino Oscillations

As a simple example, it might look something like this:

The probability of a neutrino, that starts as a �ν𝑒𝑒, acting like a �ν𝑒𝑒The probability of a neutrino, that starts as a �ν𝑒𝑒, acting like a �ν𝜇𝜇

Inverse beta decay is only sensitive to electron antineutrinos.

So acting like a muon antineutrino means that we won’t see it in our detector.

If neutrinos have mass, then the three types of neutrinos can mix with each other in a sinusoidal pattern.

1.0

⁄𝐿𝐿 𝐸𝐸νNeutrinos oscillate as a function of the distance traveled

divided their energy

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Neutrino Oscillations

0

0.2

0.4

0.6

0.8

1

0.01 0.1 1 10

ν eSu

rviv

al P

roba

bilit

y

L (km)

Electron neutrinos (and antineutrinos) undergo two types of oscillations.

The different oscillations are characterized by their amplitudes and periods:

The amplitudes tell us about the strength of the mixing.

The periods tell us about the masses of the neutrinos.

Reactor experiments have made critical measurements for both types of oscillations…

Plotted for the mean energy of detected reactor neutrinos

Short-baseline (~2 km)

Long-baseline (~60 km)

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The KamLAND ExperimentThe KamLAND experiment used neutrinos from all the reactors in Japan.

KamLAND measured the long-baseline oscillation period.

This type of oscillation had previously been observed with neutrinos from the Sun. 20

Studied the short-baseline oscillation, and measure the smallest oscillation amplitude.

The Daya Bay Experiment

Located at the Daya Bay Reactor Complex in China

Each module contains 20 tons of Gd-loaded liquid scintillator

Near detectors were used, because the reactor neutrino flux is poorly understood from theory.

In addition, the Daya Bay Experiment made measurements that have improved our understanding of reactor neutrinos... 21

Evolution of the Neutrino SpectrumAs the fuel burns in an LEU reactor, the mix of fissile isotopes evolves.

Each fissile isotope makes a slightly different set of fission fragments.

As a result, the neutrino energy spectrum is like a fingerprint for the active mix of fissile isotopes in the core. 22

Daya Bay Neutrino Spectral DecompositionUsing burn-up data from the reactor operators, the Daya Bay Reactor Neutrino Experiment used neutrinos from one of their near detector sites to decompose the spectrum for the different fissile elements.

The data clearly confirm the fissile element fingerprint hypothesis.

This study was done with detectors located 363 meters away from two cores, with out-of-sync refueling cycles.

Imagine what could be done with a detector at 25 meters, and a single core dominating the neutrino flux.

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Functionality for ApplicationsAs we just saw, neutrino detectors can track a reactor’s active fissile inventory.

In addition: The neutrino detection rate measures the reactor power.

(When averaged over hours or days, but not seconds)

An array of neutrino detectors may be able to measure the spatial distribution of fission, by triangulation.

Neutrinos can be used to detect when a reactor is on, even at a significant stand-off.

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Gathering Data on ApplicationsPhysicists have long thought that reactor neutrino detectors would find applications in reactor monitoring.

The Applied Antineutrino Physics Conference Series, has been a regular annual meeting since 2004. Unfortunately, it is mostly physicists talking to each other.

The NNSA’s Office of Defense Nuclear Non-proliferation has commission the ongoing NuTools Study (https://nutools.ornl.gov/) to engage with experts in the nuclear industry and nuclear security to assess the viability possible applications.

Last spring, I lead a team in a study of possible applications funded by the National Science Foundation’s Innovation Corps.

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https://nutools.ornl.gov/

The NSF’s I-Corps program gives inventors training, and money to gather data on commercialization of their technologies.

Participants have seven weeks to dash around the country and interview more than 100 people in the appropriate industrial sectors.

Gathering Data on Applications

Team Neutrino TechnologiesMay/June 2019

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Non-Proliferation SafeguardsIn the context of nuclear non-proliferation safeguards several possible applications have been identified:

Recovery from a loss of continuity-of-knowledge eventAfter a diplomatic break down or other interruption in monitoring, neutrinos can determine if plutonium has been removed from the reactor.

Continuous monitoring of a reactor’s operational statusIn the JCPOA, Iran’s heavy-water reactor was rendered inoperable. In future agreements short of destroying a reactor, neutrino detectors could be used that a reactor remains off.

Tracking fissile inventory in operating reactorsThis may enable verification for possible future agreements like a Fissile Materials Cut-off Treaty.

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Reactor InstrumentationPotential applications identified in reactor instrumentation include:

Neutrino calibrated ex-core neutron detectorsInverse beta decay detectors are also excellent neutron detectors. Could ex-core neutrino detectors eliminate the need for in-core neutron detectors, and thus significantly reduce the number of pressure vessel penetrations?

Tracking the fissile inventory for Gen IV reactors with liquid fuelChemical assay creates a waste stream and sample pulling is a proliferation risk. Neutrino detectors could for low-risk, continuous monitoring.

Verifying critical status of the core following a beyond design basis accidentGod forbid, if there was an accident and the plant instrumentation is off-line, neutrino detectors could be used to determine if there is an active fission reactor.

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Making Applications a RealityNuclear security and non-proliferation safeguards, particularly in situations with limited trust, have always seemed like a good starting place for applications.

But the IAEA is understandably reluctant to express a mission need requiring nonexistent or unproven technologies.

Similarly, existing commercial reactors have the instrumentation they need to satisfy regulatory requirements.

Gen IV reactors may have unique needs and an openness to innovative solutions.

So finding use cases in commercial nuclear would help to establish neutrino technologies for security applications.

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Past Reactor Neutrino Detectors

They typically used organic liquid scintillators, which tends to leak and have issues with long-term chemical stability, and flammability

These detectors were large and unwieldy.

They needed the thickest possible overhead shielding to combat cosmic-ray fast neutron backgrounds.

As a result, they were either at some standoff, in an underground cavern, or perhaps constructed in situ in a tendon gallery.

These detectors are not suitable for widespread use in applications.

So far reactor neutrino detectors have been delicate research instruments, requiring ideal conditions and constant attention.

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The CHANDLER Reactor Neutrino Detector TechnologyCHANDLER was designed, from the start, as a robust, mobile detector technology.

It uses a highly segmented array of plastic scintillating cubes as the neutrino target and positron detector, and thin sheets of lithium-6 doped zinc sulfide (ZnS) scintillator to tag neutron capture.

Light is transported along the rows and columns of cubes by total internal reflection, and readout by photomultiplier tubes.

As with the Reines and Cowan experiment, the segmentation is used to tag the gammas from positron annihilation, and thus reject fast neutron correlated backgrounds.

The MiniCHANDLER Prototype, open during assembly to show the cubes and 6Li-doped ZnS sheets 31

Deployment at North AnnaThe MiniCHANDLER prototype was installed in our Mobile Neutrino Lab, deployed to Dominion Power’s North Anna Generating Station in Mineral Virginia, and parked just outside their Reactor 2.

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Deployment at North Anna

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Fast Neutrons in MiniCHANDLER

No positron tag appliedReactor-off

The fast neutron rate is independent of the reactor power.Instead, it’s inversely correlated with the atmospheric pressure.After a correction, the average reactor-on correlated rate was found to be 4 events/hour more than with the reactor off.Which is the expected rate for neutrino events.

In this simple prototype, the positron tag improves the signal-to-noise by about a factor of five! 34

MiniCHANDLER DemonstrationMiniCHANDLER was the largest detector we could afford to build and the smallest detector with a chance to see neutrinos. We used surplus photomultiplier tubes, and we had to forgo light-guides that were shown to improve light collection efficiency by 64%.

We had no cosmic-ray shielding, and only an inch of boron loaded poly to stop thermal neutron from the reactor.

Yet, we succeeded in observing the antineutrino spectrum!

1stunshielded

reactor neutrino detector

1st mobile neutrino detector

World’s 3rd smallest

neutrino detector

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2nd smallest reactor neutrino detector

To study the impact of modern PMTs and lightguides, we rebuild our smaller prototype with half new PMTs and lightguides and half old PMTs.

Detector Upgrades

The Micro CHANDLER prototype, testing new PMTs and light guides.

511 keV Compton Edge

1273 keV Compton Edge

The energy resolution is improved by a factor of 2.

The positron annihilation gammas stand out much more clearly.

22Na Source

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Detector UpgradesAdditional planned upgrades will get us the event rates, energy resolution and efficiency needed for a range of entry-level applications.

1. Doubling the number of 6Li-loaded ZnS sheets, which has been shown to improved the neutron detection efficiency by 35%.

2. Increasing to a detector module mass to between 2 and 5 tons will accumulate events at several hundred per hour and more effectively contain neutrons and annihilation gammas.

3. Improved optics, including PMTs on four sides, will increase the signal-to-noise to better than one-to-one, while simultaneously sharpening the fissile-element specific spectral differences.

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What Comes Next?

1. Build a ton-scale detector using our best and most sensitive technology.

2. Use this detector to demonstrate the required sensitivity.

3. Deploy detector modules to a wide variety of reactor types to complete a high-resolution decomposition of the fissile-element specific spectra:• Light Water Commercial Reactor• HEU Research Reactor

4. Continue engagement with the nuclear industry to figure out how this technology can best be used.

• CanDU Reactor• MOX Fuel Reactor

• Etc.

This detector R&D program is just getting started, and there is more we need to learn about the fissile-element specific neutrino spectra.

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Conclusions1. From the original discovery experiment in 1956, nuclear reactors have played a

crucial role in furthering our understanding of neutrinos.

2. We physicists have hopes of giving back to the nuclear industry that has been so kind to us, by developing reactor enabling technologies based on neutrino detection.

3. Advances in detector technology are pointing the way to robust instruments that can operate above ground, and in the environment around an active reactor.

4. The CHANDLER technology is one such detector, and our R&D program seeks to demonstrate its full potential.

5. We need your help to identify promising use cases, and to establish the performance requirements to meet those needs.

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Upcoming Webinars17 December 2020 Development of Multiple-Particle Positron

Emission Particle Tracking for Flow MeasurementDr. Cody Wiggins, University of Tennessee, USA

28 January 2021 MOX Fuel for Advanced Reactors Dr. Nathalie Chauvin, CEA, France

25 February 2021 Overview of Waste Treatment Plant, Hanford Site Dr. David Peeler, PNNL, USA

Slide Number 1Some Housekeeping ItemsTo Ask a QuestionSlide Number 4Meet the PresenterWhat This Talk Will CoverDisclaimerThe Invention of Neutrinos Discovery of the NeutrinoReactors as a Neutrino SourceReactors as a Neutrino SourceReactor Neutrino DetectionReactor Neutrino BackgroundsReactor Neutrino BackgroundsDiscovery of the NeutrinoNeutrino Physics at ReactorsParticle PhysicsNeutrinos and Particle PhysicsNeutrinos and Particle PhysicsNeutrinos and Particle PhysicsNeutrino OscillationsNeutrino OscillationsThe KamLAND ExperimentThe Daya Bay ExperimentEvolution of the Neutrino SpectrumDaya Bay Neutrino Spectral DecompositionFunctionality for ApplicationsGathering Data on Applications�Slide Number 29Non-Proliferation SafeguardsReactor InstrumentationMaking Applications a RealityPast Reactor Neutrino Detectors The CHANDLER Reactor Neutrino Detector TechnologyDeployment at North AnnaDeployment at North AnnaFast Neutrons in MiniCHANDLERMiniCHANDLER DemonstrationDetector UpgradesDetector UpgradesWhat Comes Next?ConclusionsUpcoming Webinars